1. Field of the Invention
The invention pertains to the art of air conditioning units of the type adapted for either roof top or slab mounted installations.
2. Description of the Prior Art
There are numerous patents in the air conditioning art which disclose arrangements in which by rearranging inner partitions and/or end panels, air flow paths through the unit may be changed. Representative of such patents are the following: U.S. Pat. Nos. 2,401,560, 2,690,654, 3,156,233, 3,678,993, 3,977,467, 3,995,446 and German Pat. No. 2,414,443. However, in none of these is an arrangement shown which can attain all the objects of my invention.
However, as an aid in promoting a thorough understanding of the advantages of the arrangement of the invention, a discussion of some of the design desiderata relative to past commercial practices is considered warranted. The 1975 ASHRAE Equipment Handbook sets forth some of the matters of mechanical design of roof top units which should be taken into consideration. Among these it is noted that the cabinet height dimensions are important for roof top units since large units must be designed with consideration given to the limitations of truck bodies, freight cars, doorways, elevators and to the usual rigging practices. It also points out that the design should have sufficient structural strength to accommodate handling, warehouse stacking and shipment. Also, the cooling coil air velocities must be low enough to prevent entrainment of condensate. Service access must be provided for installation and repair, and versatility of application, such as multi-fan discharge direction and either-hand piping are valuable considerations. The handbook also points out that consideration should be given to permit various air flow options, such as air duct kits which can permit horizontal or vertical connections, and duct damper kits for control of outdoor air intake and exhaust.
Among considerations of this type to which attention was directed in accomplishing the arrangement of my invention were the following. The desired roof top unit should accommodate air flow into the indoor air flow section from either the bottom (a vertical air flow made arrangement) or from the end (a horizontal air flow mode) without requiring any added section or module as has been typical in the past. This was to be accomplished with reasonable compactness of the unit. It will be appreciated of course that if there are no limitations on how big a unit can be in any of the various directions, the matter of designing the unit to accomplish everything desired is relatively easy. However, as a rule the larger the unit the greater the cost. Further, one design restriction taken into account in my invention is that the height of the units of say 71/2 and 10 tons refrigerating capacity be limited so that two of them can be stacked one upon the other and not exceed 90 inches to accommodate shipping by truck. At the same time, the supply and return openings, wherever they are located must be of at least a given size unit, as well as the interior air flow spaces must accommodate the required volume of air without excessive fan power required. Also with the particular air flow requirements, the refrigerant coil must have at least a given face area, and provision must be made for handling condensate for when the coil is functioning as a refrigerant evaporator.
It is also considered desirable that the particular unit be such that in its standard form it can be shipped to a distributor who would stock the unit, and be within the distributor's ability to change from a vertical air flow mode to a horizontal air flow mode at his location without having to stock separate add-on box sections to achieve the change. Since various air flow control options achievable by different damper arrangements is desirable, the unit should accommodate the installation of these damper elements at the distributor's location. Finally, it is desirable that the basic construction of the unit be such that it be adaptable for heat pump operation; in which case supplemental electric resistance heat will be required ordinarily. As is well known, electric heat must be located downstream from the refrigerant coil which acts as a condenser in the heating mode of the heat pump. This is because if the electric heat were upstream of the condenser, the condenser would be ineffective to add heat to the already heated air and also would generate problems of too high condensing temperatures and pressures and a low coefficient of performance. Now with the electric heat arrangement, there still exists the alternatives of having a blow-through or draw-through arrangement with respect to the location of the blower relative to the refrigerant coil. It is considered desirable in my view that the arrangement be that of draw-through the refrigerant coil and blow-through the electric heat so that a relatively high velocity air stream available at the discharge of the blower is directed over the heaters to thereby permit a high watt density heater arrangement.
As the description proceeds, it will become apparent that at least most of the basic design parameters treated herebefore are met with an arrangement according to my invention.